EPA radon action level 4

https://fair-wiki.win/index.php/New_Study_Scrutinizes_EPA_Radon_Action_Level_and_Home_Safety_Standards

The EPA radon action level is 4 picocuries per liter of air, a threshold set to guide homeowners on when to take protective measures. If your home tests above this level, the agency recommends installing a mitigation system to reduce exposure. This isn't a safety line but a practical benchmark, since radon, a naturally occurring radioactive gas, can increase lung cancer risk over time.